Inductance coil



Nov. 10, 1953 v. E. LEGG ET AL 2,659,057

INDUCTANCE con Filed Sept. 13. 1950 FIG.

' v. 5. L566 lNI/ENTORS C- D OWENS A TTORNE V Patented Nov. 10, 1953 INDUCTANCE COIL Victor E. Le s, Maplewood, and Conrad D. Owens,

Chatham',

J., assignors to Bell Telephone Laboratories, Incorporated New York, N; Y., a

corporation of New York Arpplication September 13, 1950, Serial No. 184,602

3-Claims. l.

Thisxinvention'relates' to inductance coils and more particularly to such coils especially suitable for use'in channel'fil-ter circuits' -fo'r broad-band carrier systems. I

In one such system, twelve channel fil ters'm-ay be: employed to select the lower sideband-derived from the modulation 015 speech signals and carrier frequencies spaced every four kilc'cyoles' in a frequency-"range of from sixty-four to one hurl-- dred. and eight kil'ocycles. Inductance c'oilsa're associated with these channel filters and because of: the? close spa'cing of the channels it is advantageous that the inductance of these coils be both very accurately initially determined and also be very stable. High Q, which is ratio of reactance: of resistance; andlgo'odf stability in the coil are desi'red' to" give the requiredselectivity under operating conditions; The very precise adjustment of the' filterby proper adjustment of the inductance" of thecoil vis advantageous to tune the" filter exactly-to the desired frequency band.

In prior coils employed with channel filters accurate: adjustment of the" inductance has been attempted by selecting or 'adjust'ing the number of turns in the winding 'orby' varying thelength or size of air gapsinthe magnetiecircuit. The former. method; has been used? primarily with coils wound toroidally; 'on sin'glepiece iringcoresi by which: adjustment can be madeto'th'e nearest' whole: turn. The latter' method' is applicable to: cores assembled from two or: more: ma netic:

members-e Thismethod-I of: course requires? very accurate: mechanical dimensioning involi/ing pre cise grinding operations; Such grinding. has cer tain inherent disadvantages; andz'particul'arlyso when? the core materialris of the-ceramic ferro magnetic material known as ferrite which;is"ad vantageously employed: because of its very high permeability and low losses: butzwhich requires specialgrindingtechniques because of" its hard"-" ness. Butgrinding corestodimensions for ad justment is to be avoided for the additional reason that iflthe inductance of a coil when assembledisnot within the prescribed limits it is necessary to take the coil apart to perform the grinding operation and then to reassemble it, withpossible minuteivariations entering because of ithe difierent orientation of the coil members when? reassembled, in additionto the delay and expense: of repeated reassemblingand the increased possibility of faulty assemblings:

It has also beenpriorlyproposed to adjust the inductance of themagnetic circuit-by introducing or withdrawing-magnetic members. from airgaps in they magnetic circuit, Ithas been foundl however, that this causes harmful concentrations of magnetic flux in'the portionof the magnetic member inserted into the air-gap causing a decrease in the Q of the coil and that it is difiicult to'mechanic'ally secure the moving membersufliciently to insure high stability'of the magnetic circuit. Thusin order to maintain the desired Q and stability of the coil it hasbeen-foun'd clesirable to maintain a predetermined air ga'p.

In addition to very finely adjusting thei'riductanc'e of the coil to tune the filterlto' the de? sired frequency band and to maintaining its high Q to give the desired seleotivity,-it is also desirable to completely enclose-the core within the magnetic circuit to minimize possible flux" leakage which could provide coupling with the other equipment andcoils of thecha'nnel' bank. When inserts into the air-gap are employedtoa'ccurately determine the inductance ofthe' coil either they mustextend' in some-Way through the'm'a'g netic casing around the coreorth'e casing must be taken apart and reassembled] each timeflthe position of the insert is -varie'd during the final adjustment of the inductance; Additional pcr'fo rations of the'mag'neticcasing are, however, undesirable if flux leakage is to be minimized" arid repeated d-isassemblings and reassemblingsare' to be avoided as time consuming an'd as too prolific asQu'rGe ot inaccuracies in thevalue' of" the inductance; Further ferrite does not easily lend itself' to accurate perforations or'close edgessuoh as" would be requiredfor any threaded p'e'ri'ora tion's if the adjustments were to bemade" by threaded-'means extending through the; casing".v Itis aILobject-bf this invention to adjust the v inductance of such coilsfacilely and accurately;

A fur'the'r'object of this ihyention is" to adjust the inductance of such coils -accurately 'without altering the sizeof theair-gaps" or other ele' ments of the magnetic circuiti varying th'eposition of' any insert's 'in 'such air-gaps; or' in" other wayslalteriiig the m'a gnetic circuit or affecting the" stability thereof.

Aifurthe'robject of thisinvehtion is 'to reduce to a 7 minimum the number of 'perforations" that must be made iri the magnetic casing surrounding the coil and further to reduce-to a minim m-1 the number of adjusting controls and mechanical parts re'q'uired."

A further objecfiofthislilviitldh is tbive iy" finely adjust the inductance of such coils wlth'ouif accordance with: 'one speoific embodiment o f this invention in a coil comprising a pair of cup shaped members of ferromagnetic material, such as ferrite, joined together to form a casing enclosing the winding. The winding is wound on a spool securely mounted on a hollow center post of ferromagnetic material. lihe center post, which completes the magnetic circuit, is rotatably supported along the axis of the casing. One end of the winding extends through an aperture at the center of the base of one of the cups and the other end extends through an aperture in the side of one of the cups adjacent the juncture of the two cups. Predetermined air-gaps are provided between the center post and the ends of the casing by the spacers rotatably supporting the center post.

When the coil is assembled and the two cupshaped members firmly fastened together, a spindle is introduced through one end of the casing into the hollow center post. The inductance of the coil may then be accurately adjusted by changing the number of turns of the winding, the outer end of the winding extending through the side of the casing being pulled to rotate the winding form and center post on the spindle thereby unwinding a portion of the coil. The coil may be rewound if necessary by turning the spindle extending into the center post.

After adjustment of the inductance, the center post and Winding may be immobilized in any of several ways, such as by cementing the outer end of the winding securely in the casing, by injecting acement or binder into the casing, or by a mechanical clamping.

In another specific embodiment of this invention adapted to be end mounted, the spindle to rotate the center post forms part of the insulation surrounding the one end of the coil extending axially out of the casing. A second spindle permanently extends into the casing and into the center post, thus serving to position the center post and prevent sidewise movement of it. The other end of the winding is also brought out through the one end of the casing. The inductance is adjusted by pulling the outer end of the winding and by rotating the knob on the combined spindle and insulator surrounding the inner end of the coil to alter the rotational position of the center post.

It is one feature of this invention that the winding be supported in an enclosed casing by a rotatable center post, that one end of the winding be brought out along the axis of the center post, and that other end of the winding be brought out through the casing in such position as to effect rotation of the center post when that other end of the winding is pulled.

It is a further feature of this invention that the center post be hollow and that there be an aperture in the casing end along the axis of the post opposite from the end through which the one end or the winding is brought, the hollow post being formed to receive a mating spindle which is insertable therein.

A complete understanding of this invention and of the various features thereof may be gained from consideration of the following detailed description and the accompanying drawing, in which:

Fig. 1 is a perspective view of an inductance coil illustrative of one embodiment of this invention;

illustrative of another embodiment of this invention.

Referring now to the drawing, the casing com prises two cup-shaped members II and I2 of magnetic material; specifically the cup-shaped members may be of a ceramic ferromagnetic material, such as is known as ferrite and may specifically be of a manganese-zinc ferrite. A center post I3, which may also advantageously be of ferrite, is positioned axially in the casing and forms together with the casing the magnetic circuit of the coil. The post is positioned in the casing by the apertured spacers or washers I l and I5, which may be of paper or other insulating material, between it and the base of the cup-shaped members. These spacers provide bearing surfaces for the post 13 so that it is free to rotate inside the closed cylindrical casing. The winding I6 is wound on a spool I! which is cemented directly to the center post [3 and therefore is free to rotate with the post. One end iii of the winding is brought out through an aperture in the base of cup-shaped member l2, the end extending through the spacer l5. Insulator I9 surrounds the end is and may be secured to the post I 3 as by a cement 2D. The other end 21 of the winding is brought out through the side of the casing, as through an aperture 22 in the cup-shaped member l2 adjacent the side of the casing where the two cup-shaped members are joined together. An insulating grommet 23 is positioned in the aperture around the end 2|.

Two end plates 25 and 2B fit against the bases of the casing and are clamped together by the screws 21 and nuts 28, thereby clamping the coil in compact assembly.

After the coil has been assembled, a spindle 39, which may be of Lucite, is inserted through an aperture in the cup-shaped member H, the spacer M, and into the hollow center post. Adjustment of the inductance of the coil is then accurately made by pulling the end 2| of the winding I6 to rotate the spool I! and center post iii, to which it is joined, as a reel, the spindle providing an axis of rotation and preventing any transverse motion of the post.

The inner end portion 3| of the spindle 30 is serrated to grasp the inside of the hollow post l3. Thus the end 2| of the coil 16 can be rewound on the spool I! by turning the handle 32 of the spindle 30 to rotate the post I 3 in the opposite direction.

The outer end 21 can be secured after the accurate adjustment has been made as by being cemented to the grommet 23 or in any of the other ways mentioned above. The spindle may also be removed after the fine adjustment has been made.

In one specific embodiment of this invention that was constructed as illustrated in the drawing, the change of inductance with the number of turns unwound was found to be as follows:

Percentage change in L Induc- Comolcte Turns Number tance L Unwound of Tums (Micro- Total henrics) One (Based on Turn initial value) 42 938. 4 41 890. 6 5. 2 5. 2 40 841. l 5. 5 l0. 4 39 798 5. 4 15. O 38 758 5. 0 l9. 3 37 717 5. 4 23. 6 36 677 5. 6 27. 8

These data were taken at a testfrequenc of 100 kilocycles andwith a currentof .001 ampere. While, as the table shows, the inductance was changed approximately 5 per cent per turn, the inductance could; readily be adjusted to any smaller percentage or value equivalent to a very small fractional unwound The inductance in fact is easily adjustable to any desired. value within the order of a. microheI-rry for the winding described. The precision of adjustment-de pendspartially upon the: accuracy with: which the rotation. of the center post can be set and the number of turns: in the winding. Micrometric adjustment of the. post position. could be obtained by suitable mechanical. means if desired. While the inductance is thuscapable of being: very accurately set over a. wide range, the per cent change in the Q-oi the coil concomitant the inductance change is very small, being less than 5 per cent for the approximately 30 per cent inductance change shown.

When the coil is. assembled there will normally be no need to change the inductance by 30 per cent. Instead the. core structure may .be assembled from parts of merely nominal dimensions, thereby obviating the necessity of accurately dimensioned parts or the necessity for adjustment of air-gaps by precise grinding and trial and error assembly. When assembled a. rough frequency adjustment can be made in the shop,

which will generally require only the removal or addition of a few turns at most. The outer end 2| can be clipped to a nominallength and tinned, but left loose in the grommet 23. A final fractional turn adjustment to attain the high degree of accuracy'desired' can then be made during, the assembling of the filter unit, after which the end 2! and spool IT can be secured in any of the manners discussediherein.

However, the large changes. of inductance of -55 the coil that may be made varying the number of turns, as shown by the above exemplary data, affords another advantage in this novel structure and the inductance adjustments possible thereby. In many filter applications, such as in certain channel filters whether employing crystals or not, the circuit design will advantageously require a number of inductances in the circuit of similar but slightly different inductances. coils on either side of a capacitance, forming a T-unit of the filter, may vary by from 5 to per cent. However, by employing coils constructed in accordance with this invention the same component part may be used and each coil mere- 1y adjusted to the difierent inductances in the fabrication of the coils in the shop, as explained above. These coils can then be directly incorporated into the filter, or if used to accurately tune the filter, can be finely adjusted in the circuit as explained above. However the whole series of coils employed, each having a slightly different inductance, may all be fabricated from the same piece parts and with the same predetermined optimum air-gaps, with concomitant savings in the cost of the coils and improvements in their electrical characteristics.

Various modifications may be made without departing from the scope of this invention. The spindle 30 may be replaced by a fluted key which will lock the spool I! when pushed in, but will permit the spool to rotate when pulled partially out. In that instance the key will remain in the post I3, whereas the spindle 30 may be removed after the inductance has been permanently ad- Thus the inductance between successive justed to the desired value. If a fluted key is employed the post l3 and spool f-l must be rotated in discrete distances each timeso that the fluted key can fit inside the fluted holes or bushings in the ferrite parts; however the number of sides to the key could be made sufficiently large so: that the steps would be small enough to permi-taccurate adjustment: of the inductance.

The spool 11 may also be securediagainst. undesired motion after ad'justment of the inductance by providing'notched or serrated edges to the spool ends, these detents to engage. a knob-or boss on the inside ofv the casing. Alteration of the number .of turns of the winding. 1 6 would then adjust the inductance to a. sequence of closely spaced values dictated by the closeness of thedetent notches on the spool ends.

The rotation of the spool 11 and winding Hi may be further facilitated by mounting the. center post l3 on bearings, as of phenol fibre tubing or rod, to serve as a permanent internal shaft extending from .holes in the center post through holes in the casing. The inner end H! of the winding l6 could then be brought out through the tubing or rod at the one end of the casing and a. screw-driver slot could be placed in the tubing or rod at either end of the casing to permit rewinding of the coil if necessary.

If it is desired to have a single side mounted coil with mounting studs, terminals, and adjusti-ng means all located on one end of the casing, the outer end. of the winding may be guided out through the end of the casing instead of the side and the insulation surrounding the inner end .of the winding could be incorporated into a spindle and employed to rotate the center post. One illustrative embodiment of this invention incorporating these features is shown in Fig. 3. Referring now to thatv figure, the casing comprises the two cup-shaped members I] and I2 in which is centrally located the. center post 13 positioned by the end spacers or washers l4 and [5. The winding I6 is wound on the spool 11 on the center post. The inner end 18 of the winding extends through an axial aperture in the base of the cupshaped member I! and is surrounded by an insulating sleeve 35. The sleeve has an inner portion 31 directly secured to the center post I3, as by a cement 38, and has a serrated knob 36 attached to it. The sleeve 35 can thus itself be rotated to alter the rotational position of the center post [3 and thus the inductance of the coil.

The outer end of the winding "5 is brought out through an aperture 40 also in the base of the cup-shaped member l2 but adjacent the periphery thereof. An insulating grommet 4| surrounds the end IS in the aperture 40.

A phenol fibre rod 42 extends axially through the cup-shaped member I l into the center post 13 and serves as a permanent internal shaft to position the center post and prevent sidewise motion of the center post.

Adjustment of the inductance of the winding and immobilization of the center post are achieved as described above with reference to the embodiment of Fig. 1. However the adjustment may be made after the coil has been end mounted, by the mounting studs 43 on the bolts or screws 21, as both ends of the winding extend through the one end of the cup-shaped member I2.

It is to be understood that the above-described arrangements are illustrative of the application of the principles of the invention. Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. An inductance coil comprising an enclosed cylindrical casing of a ferrite material, said casing having apertures at both ends along the axis thereof and an aperture through one side thereof, a single rotatable core of a ferrite material axially in said casing between the ends thereof, a spacer member rotatably positioning said core closely adjacent each of said ends and determining airgaps between said core and said ends, a spindle secured to said core and rotatable therewith, and a winding on said spindle, said core and said winding substantially completely filling said cylindrical casing, one end of said winding extending through one of said end apertures and the other end of said winding extending through said side aperture whereby the inductance of said winding may be varied by pulling said other end to rotate said core and reduce the number of turns of said winding on said spindle, the portion of said winding removed from said spindle being brought outside of said casing.

2. An inductance coil in accordance with claim 1 wherein said rotatable core has an aperture axially therein cooperating with the other of said end apertures to allow a tool to be inserted into said core to rotate said core in the other of said directions to increase the number of turns of said winding on said spindle if too many of said turns have been removed by pulling said other end.

3. An inductance coil comprising a first cup member of a ferrite material having an aperture centrally in the base thereof, a second cup member of a ferrite material having an aperture centrally in the base thereof, one of said cup members having a second aperture adjacent the lip thereof, means securing said cup members together to form an enclosed casing, a single rotatable center post of a ferrite material axially in said casing, said center post having a central aperture axially therethrough and communicating with the apertures in the bases of said cup members, a pair of washers rotatably positioning said center post closely adjacent the bases of said cup members and determining the air-gaps between said post and said bases, a spool secured to said post, a winding on said spool, said core and said winding substantially completely filling said casing, one end of said winding extending through one of said washers and the aperture in the base of said first cup member, the other end of said winding extending through said side aperture, an insulating grommet in said side aperture surrounding said other end whereby said post is rotated in one direction to reduce the number of turns on said spool by pulling said other end to bring a portion of said winding through said side aperture outside said casing, and a rod member extending into said central aperture in said post through the second of said washers and the aperture in the base of said second cup member for rotating said post in the other direction to increase the number of turns of said winding on said spool if too many of said turns have been removed from said casing, whereby the inductance of said winding may be very accurately adjusted.

VICTOR E. LEGG. CONRAD D. OWENS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,158,123 Fessenden Oct. 26, 1915 1,555,509 Marrec Sept. 29, 1925 1,668,414 Martin May 1, 1928 1,936,671 Hurt w. Jan. 3, 1931 FOREIGN PATENTS Number Country Date 728,756 France Apr. 18, 1932 

